Color cathode ray tubes of the shadow mask type

ABSTRACT

In a color cathode ray tube including a shadow mask assembly comprising an interfitted rectangular shadow mask and supporting frame, each having four rounded corners, the radius of curvature of the four rounded corners of the side wall of the shadow mask is made smaller than that of the four rounded corners of the supporting frame.

United States Patent Kawamura [45] Nov. 21, 1972 s41 COLOR CATHODEIRAY TUBES OF THE SHADOW MASK TYPE [72] Inventor: Takao Kawamura, Chiba-ken,

Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Jan. 7, 1971 211 Appl. No.: 104,561

[ 1 Fordsnrr g q Priqritrpata Jan. 7, 1970 Japan ..45/2l47 [52] US. Cl. ..3l3/85 S, 313/72 B [51] Int. Cl ..H0lj 29/46, HOlj 29/56 [58] Field of Search ..313/85, 85 S, 92 B [56] References Cited UNITED STATES PATENTS 2,939,931 6/1960 'Hoagland 313/85 7 3,588,567 6/1971 MacLean et al ..313/85 S Primary Examiner-Herman Karl Saalbach Assistant Examiner-Saxfield Chatmon, Jr. Attorney-Craig, Antonelli & Hill [5 7] ABSTRACT In a color cathode ray tube including a shadow mask assembly comprising an interfitted rectangular shadow mask and supporting frame, each having four rounded corners, the radius of curvature of the four rounded corners of the side wall of the shadow mask is made smaller than that of the four rounded corners of the supporting frame.

7 Claims, 5 Drawing Figures lZ7/%7/7/7 aw/7,07%

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ATTORNEY5 COLOR CATHODE RAY TUBES OF THE SHADOW I MASK TYPE BACKGROUND OF THE INVENTION This invention relates to a color cathode ray tube of the shadow mask type, and more particularly to such a color cathode ray tube including a shadow mask assembly according'to which it is possible to quite efficiently utilize the entiresurface of the rectangular face plate of the tube.

In the conventional color cathode ray tube of the shadow mask type, the shadow mask, which is of substantially rectangular. configuration and having rounded corners, is supported by a support frame of similar size and shape tothe periphery of the shadow mask and also having rounded comers. Thus, the periphery of the shadow mask can fit snugly into the support frame and is thereby firmly supported therein.

However, the support frame, due to its function, of necessity must be heavier and of thicker construction than the shadow mask, and therefore, it has been very difficult to form rounded comers of small radius into the support frame without producing crimping. Because of this problem, it has been difficult to provide such cathode ray tubes with rectangular screens without losing the use of some portions of the screen.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide an improved color cathode ray tube of the shadow mask'type containing a shadow mask assembly which makes it possible to 'use a rectangular face plate.

Another object is to provide an improved shadow mask assembly according to which it is possible to reduce as far as possible the radius of curvature of the round corners of the shadow mask thus making it possible to scan all of the corners of the rectangular face plate of the cathode ray tube with the electron beam.

According to this invention in a color cathode ray tube employing a shadow mask assembly of the type referred to above, the radius of curvature of the four rounded corners of the side wallof the shadow mask is made smaller than that of the four rounded comers of the supporting frame.

BRIEF DESCRIPTION OF THE DRAWINGS The invention can be more fully understood from the following description taken in conjunction with the acv companying drawings in which:

FIG. 1 shows a longitudinal section of a prior art color cathode ray tube of the shadow mask type;

FIG. 2 shows a section, partly broken away, of the cathode ray tube shown in FIG. 1 along line II--II;

FIG. 3 is a partial enlarged sectional view taken along line III-III in FIG. 2;

FIG. 4 is a view similar to FIG. 2 showing a shadow mask assembly embodying this invention; and

FIG. 5 is a partial enlarged sectional view taken along line V-V in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT As is well known in the art, a conventional color cathode ray tube of the shadow mask type, as seen in FIGS. 1-3, generally comprises an evacuated glass envelope 3 having a face plate 1, a triad phosphor screen 2 coated on the inner surface of the face plate for providing three basic colors, a shadow mask 4 disposed close to the phosphor screen, a frame 5 for supporting the shadow mask, an electron shield 6 supported by the frame5, and an electron gun for producing an electron beam, as schematically shown'in FIG. 1-. Generally, the shadow mask is made of an iron plate of a'thickness of about 0.15 mm, and as shown in FIGS. 2 and 3, comprises a central dome 7 having hundreds of thousands of perforations and a side wall 8 formed by bending at right angles the periphery of the central dome 7. Since the mask is very thin as described above, it is necessary to use the supporting frame 5 for reinforcing the same. Usually such a reinforcing frame is formed by preparing an elongated iron strip having substantially the same length as the inner periphery of the side wall of the shadow mask, bending the strip to have an L- shaped cross-section, bending the strip into an annulus, welding together the opposite ends of the strip and pressing the annulus to cause'it to conform to the substantially rectangular configuration of the periphery of the shadow mask. Then, the side wall 8 of the shadow mask is fit over the side wall 9 of the support frame 5 to complete a shadow mask assembly, which is mounted in the envelope 3 by engaging leaf springs 10 secured to the side wall 9 of the frame 5 with pins 11 projecting from the inner wall of the envelope. The electron shield 6 is provided to extend from the periphery of the frame 5 to the inner wall 12 of the face plate 1 so as to prevent electrons from flowing into the space between these members.

In the conventional color cathode ray tube of the shadow mask type described above, in order to obtain a close fit between the shadow mask and the reinforcing frame, the four rounded corners of theside wall 8 of the shadow mask 4 and those of the reinforcing frame are shaped to have the same radii of curvatures R, and R and the closer the configuration of the face plate is to a rectangle, the more it is necessary to make smaller the radii of curvature. However, when an iron piece having a thickness of 2 to 3 mm, a width of about 10 mm and a height of about '20 mm is bent longitudinally to have an L-shaped cross-section and then bent into a rectangular frame, crimps are formed at the bends so that it has been impossible to reduce the radius of curvature of the frame to a value smaller than about40- mm. This problem makes it difficult to shape the face plate of the cathode ray tube to have a rectangular configuration.

With reference nowto FIG. 43 of the accompanying drawings, there is shown a sectional view similar to FIG. 2 of a shadow mask assembly of the novel color cathode ray tube wherein corresponding elements to those shown in FIG. 2 are designated by the same reference numerals. As in the conventional shadow mask, the shadow mask employed in this invention comprises a perforated central dome and a side wall formed by bending the peripheral portion of the dome, and the shadow mask is supported by a reinforcing of supporting frame. According to this invention, however, the radius of curvature R at the four rounded corners of the shadow mask is made smaller than the radius of curvature R at the four rounded comers of the supporting frame so as to leave small gaps between the side wall of the shadow mask and the side surface of the supporting frame at their four comers.

More particularly, the radius of curvature R, at the four corners of the frame 5 is made sufficiently large so that crimps will not be formed therein, as in the conventional design. In the above-described example for preparing the frame by bending an iron piece having dimensions of 2 to 3 mm thickness, about 20 mm wide and a height of about 20 mm, the radius of curvature R, equals about 40 mm. On the other hand, the radius of curvature R at the four corners of the side wall 8 of the mask is made sufiiciently smaller than the radius R: of the frame, for example, 25 mm. Consequently, when the shadow mask is fitted over the supporting frame, gaps are formed therebetween at four comers, as indicated at 13 in FIGS. 4 and 5.

It was confirmed by experiment that these corner gaps do not interfere with the characteristics of the color cathode ray tube. Except for these four corners, the interfitted side walls of the shadow mask and the supporting frame are spot-welded at to 30 points, thus facilitating the mounting of the shadow mask on the supporting frame as well as the reinforcing of the former. In addition, according to this invention, it is possible to make the radius of curvature at the four corners of the side wall of the shadow mask sufficiently small without regard for the limit of bending of the supporting frame, so that it becomes possible to scan corners of the face plate of the cathode ray tube with the electron beam, this facilitating the provision of a rectangular face plate.

It should be understood that the invention is not limited to the specific embodiment illustrated and that many changes and modifications may be made within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a color cathode ray tube of the shadow mask type comprising an evacuated envelope having a face plate at one end, a fluorescent screen on the inner side of said face plate, means for generating an electron beam for scanning said fluorescent screen, and a shadow mask assembly disposed close to said fluorescent screen across the path of said electron beam, said shadow mask assembly including a rectangular shadow mask having four rounded corners and a rectangular supporting frame having four rounded corners and having its outer wall fitted to the inner wall of said shadow mask, the improvement wherein the radius of curvature of the four comers of the side wall of said shadow mask is made smaller than the radius of curvature of the four corners of said supporting frame.

2. The color cathode ray tube according to claim 1, wherein the radius of curvature at the four comers of the side wall of said shadow mask is approximately 25 mm, whereas that of said frame is approximately 40 3. The color cathode ray tube according to claim 1, wherein interfitting side walls of said shadow mask and said supporting frame are spot-welded except at said four comers.

4. The color cathode ray tube according to claim 3, wherein the number of said spot-welded portions is 10 5. The color cathode ray tube according to claim 1,

further comprising pins mounted on the inside wall of said envelope and leaf springs secured to said supporting frame, wherein said shadow mask assembly is supported in said envelope by engaging said leaf springs with said pins.

6. The color cathode ray tube according to claim 1, wherein said supporting frame further supports an electron shield.

7. In a color cathode ray tube of the shadow mask type comprising an evacuated envelope having a face plate at one end, a fluorescent screen on the inner side of said face plate, means for generating an electron beam for scanning said fluorescent screen, and a shadow mask assembly disposed close to said fluorescent screen across the path of said electron beam, said shadow mask assembly including a rectangular shadow mask having four rounded corners and a rectangular supporting frame of an L-shaped cross-sectional configuration, having four rounded comers and being fitted to the periphery of said shadow mask, the improvement wherein the radius of curvature of the four corners of the side wall of said shadow mask is made smaller than the radius of curvature of the four corners of said supporting frame. 

1. In a color cathode ray tube of the shadow mask type comprising an evacuated envelope having a face plate at one end, a fluorescent screen on the inner side of said face plate, means for generating an electron beam for scanning said fluorescent screen, and a shadow mask assembly disposed close to said fluorescent screen across the path of said electron beam, said shadow mask assembly including a rectangular shadow mask having four rounded corners and a rectangular supporting frame having four rounded corners and having its outer wall fitted to the inner wall of said shadow mask, the improvement wherein the radius of curvature of the four corners of the side wall of said shadow mask is made smaller than the radius of curvature of the four corners of said supporting frame.
 1. In a color cathode ray tube of the shadow mask type comprising an evacuated envelope having a face plate at one end, a fluorescent screen on the inner side of said face plate, means for generating an electron beam for scanning said fluorescent screen, and a shadow mask assembly disposed close to said fluorescent screen across the path of said electron beam, said shadow mask assembly including a rectangular shadow mask having four rounded corners and a rectangular supporting frame having four rounded corners and having its outer wall fitted to the inner wall of said shadow mask, the improvement wherein the radius of curvature of the four corners of the side wall of said shadow mask is made smaller than the radius of curvature of the four corners of said supporting frame.
 2. The color cathode ray tube according to claim 1, wherein the radius of curvature at the four corners of the side wall of said shadow mask is approximately 25 mm, whereas that of said frame is approximately 40 mm.
 3. The color cathode ray tube according to claim 1, wherein interfitting side walls of said shadow mask and said supporting frame are spot-welded except at said four corners.
 4. The color cathode ray tube according to claim 3, wherein the number of said spot-welded portions is 10 to
 30. 5. The color cathode ray tube according to claim 1, further comprising pins mounted on the inside wall of said envelope and leaf springs secured to said supporting frame, wherein said shadow mask assembly is supported in said envelope by engaging said leaf springs with said pins.
 6. The color cathode ray tube according to claim 1, wherein said supporting frame further supports an electron shield. 